This is a study of passive intermembrane transfer of intrinsic proteins. Three specific aims are addressed: identification of the molecular properties that distinguish proteins that transfer from those that do not, development of protein transfer from model membranes to cells as a noninvasive means of modifying the transport and antigenic properties of biological membranes, and examination of mixtures of natural membranes under conditions where protein exchange might be expected to occur. The proteins under study are the anion transport protein of the human erythrocyte membrane, a histocompatibility antigen derived from mouse spleen, and surface marker antigens found in lymphocyte cell lines in tissue culture. Each of these species can be detected with extremely high sensitivity by complement fixation or assay of membrane anion permeability, measures which reflect on the proteins' native orientation and function in the membrane. Transfer of these species between model membranes and cells will be studied, and physical parameters controlling the rate and extent of functional protein transfer examined. The possibility of cell-to-cell transfer will be explored for normal and transformed cells in culture, and mechanisms whereby normal cells might control such events in vivo will be examined. The overall objective is to evaluate passive protein transfer as a mechanism for modification of membrane properties, either in natural processes or as a research instrument.